You probably already know that engine was made on 15 February, 1984, which means it has Magnetron electronic ignition. Here is the Illustrated Parts List:
http://bsintek.basco.com/BriggsDocumentDisplay/Z6mmyAVJ1DajI.pdfHere is the Operator's Manual:
http://bsintek.basco.com/BriggsDocumentDisplay/lrwBF-wU7eL7hAxB91ObQ.pdfThe engine has a horizontal crankshaft and is designed to be flange-mounted.
If you look at Page 7 of the Operator's Manual, in the left column at the top of the page, you'll see the instructions for adjusting the mixture - it is a main jet adjustment, not an idle adjustment. I'd guess you will need to adjust the mixture screw about an eighth of a turn anticlockwise, but you'll soon find out when you follow the procedure in the manual. It also tells you to set the idle speed for 1,750 rpm. Be sure the engine is warmed up for at least 5 minutes, and the choke is pushed all the way in, before you make either adjustment. It is usually convenient to use a simple tachometer with a sensing wire which wraps around the spark plug lead, similar to this one:
http://www.ebay.com.au/itm/Engine-D...DefaultDomain_15&hash=item5d51922c4eHowever you'll find there are some hundreds of suppliers of this or similar instruments on ebay.
